By Edgar A. Silinsh, J. Eiduss
This ebook is predicated at the result of decades of experimental paintings via the writer and his colleagues, facing the digital homes of natural crystals. E. Silinsh has performed a number one position in stating the significance of the polarization strength by means of an extra provider, in identifying not just the nature of the provider mobility in natural crystals, yet in settling on the band hole and the character of the all-important trapping web site in those crystals. The one-electron version of digital conductivity that has been such a success in facing inorganic semiconductors is singular ly unsuccessful in rationalizing the bizarre actual homes of natural crystals. A many-body idea is needed, and the experimental manifestation of this is often the significant function performed by way of the crystal polarization enerqies in moving the implications acquired with the remoted molecule, to the cast. The cautious reviews of E. Silinsh during this box have proven tn element how this polarization power develops round the extra service (and additionally the hole-electron pair) sitting on a molecular website within the crystal. as with every insulators, trapping websites playa dominant function in decreasing the importance of ~he present that could theoretically go through the natural crystal. it is often the case that those trapping websites are energetically dispensed in the forbidden band of the crystal. for a few years, an exponential distribution has proven itself to be beneficial and fairly right: However,' E.
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Extra resources for Organic Molecular Crystals: Their Electronic States
It is curious to observe that for more than a decade the band theory served as a Procrustian bed into which, figuratively speaking, such tender "victims" as' organic crystals were forced to fit the rigid "bed" of germanium or silicon lattice. 1 Band Theory Approach It is generally believed that the presence of translational symmetry in a crystal is a sufficient condition for applying band theory; however, this condition is necessary, but not sufficient. The other important condition is that the interaction of particles in a solid should be sufficiently strong.
14). 53 a. Such configuration causes considerable overlap of ~ orbitals (cf. 15), and consequently, considerable interaction. In other aspects the crystal structure is similar to that of anthracene: it is monoclinic, belongs to space group P2 1/ a , except that there are four molecules in a unit cell (Z = 4). 27. 122]. 7. In recent studies JONES et al. 122] have estimated the existence of two phases of pyrene crystals: the well-known phase at room temperature pyrene I, stable above 120 K; and pyrene II which is formed in a phase transition below 120 K.
110]. Perylene may thus be regarded as a "translational" compound between the A and B types of aromatic crystal structure. From this point of view it can be regarded as an excellent model compound. 7. 4 Specific Properties of Electronic States in a Molecular Crystal Weak intermolecular interaction forces (cf. 3) produce only slight changes in the electronic structure of molecules upon formation of the solid phase, and molecules retain their individuality. Thus, X-ray analysis of electron density distribution shows that electronic configuration of the molecules remains practically unchanged in a crystal.